Since the development of the Gatling gun, externally powered weapons have been proving their worth to the armed forces. Modern day weapons of this type are typically powered by electric motors. The chief advantage of externally powered weapons over other automatic weapons is the ability to easily change the rate of fire of the weapon. This may be accomplished by simply changing the speed of the electric drive motor. Such weapons also achieve higher rates of fire than gas operated automatic weapons.
Externally powered weapons do not utilize the energy developed by the detonated cartridges to activate the weapon system. For example, in U.S. Pat. No. 3,548,709 issuing Dec. 22, 1970 for Firing Mechanism for Automatic Grenade Launcher, a rotating drum with helical cam track reciprocates the barrel to open and close the breech. Such weapons will continue to cycle even though a chambered cartridge has not fired. This eliminates the possibility of a weapon stoppage due to a misfire, but may lead to a very hazardous situation. Occasionally a round of ammunition will not fire within the prescribed limits of time after the firing pin falls. The extraction and ejection sequence progresses just as if the round had fired. The extracted round may then detonate, presenting a hazardous situation to the weapon operator and any other personnel in the vicinity. This condition is called a hang-fire.